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Rebuild now wont run

J

jesusjeep19

NAXJA Forum User
Location
Susanville
1993 Cherokee 2.5
I did a complete rebuild(new everything + head work) on my engine with in the past couple months. I put it in and made sure everything was plugged in. I aligned the new distributor before I put the motor in so I am almost certain its timing is perfect. The problem is the motor wont fire. It cranks easily and forever but wont fire. An occasional backfire is the only symptom. Its got spark, fuel pressure, and compression. What are some things I could look for/test?
And one more thing. This is the only plug I couldn't find a use for. Any ideas?
S5030860.jpg
 
Since you get a backfire, you are getting spark, so it is most likely not the CPS. I vote on the distributor being 180 out. Make sure the ground from the rear of the head to the firewall is there and intact.
 
I was thinking it was the distrib 180 out too. So Ill go check that. Ill make sure I have a good ground back there too. Any ideas on that plug though? Thanks for the help.
 
Ok, the ground is good. As for the spark, I tried rotating the plug order 180(move 1 to 4 and 3 to 2 and vice versus) and then the motor started trying to run. It would barely start running but then die back down to just cranking. If I gassed it while cranking it would mildly sputter but still no avail. So I put the plugs back to there origional positions and rotated the distrib 180. Now the motor just cranks, and occasionally while cranking the motor will sort of pulse(warning lights dim, cranking slow, all of which only for a second). So could my distrib just be way out of alignment? I guess I am just going to have to pull the a/c compressor off and align everything to TDC.
 
Ok, timing is perfect. I have aligned the distrib to TDC. But it still just cranks. Now it isnt even backfiring or pulsing. It just simply cranks. So could it be the CPS? if it is, where is this sensor and how can I test it?
 
I'm not sure by reading but did you find TDC on #1 and then move the timing mark back so the balancer and the marks were alined???

After that you put the distributor back in.
 
Yes that is what I did. I got TDC by alligning the balancer with the marks on the timing chain cover, then aligned the distrib shaft with the cap.
 
I am a newb bigtime, but I just found out last nite and today, If the CPS isn't positioned just right, I read somewhere today .82mm, the weaker pulse will keep Renix in open loop, and depending how weak (missed pulses?) it fires all injectors tring to locate timing. I thought it was fuel.
Just held down hard on the CPS while I tightened it.
I was always told it was start or not with the CPS.
 
Last edited:
I just pulled it off and cleaned it really good. It was covered in grease. I made sure it was on real tight afterwards. But the motor still does the same thuing. Just cranking. So I unplugged the negative cable and now im letting it sit for half an hour to see if the computer will reset itself. If this dosnt work then I am just going to replace the sensor.
 
Yes it is aligned very well. Well even after reseting the computer, it still dosnt run, and a new CPS is 70 bucks so I am gonna see if I can get the one of my brothers XJ.
 
you guys are freaking me out. I'm in tear down mode on my 89 renix, and I'm really not looking forward to the re install. what the hell is a cps? am i all worked up over nothing?
 
Ok, update. To test the CPS I unplugged it and cranked the engine over. I got no spark. I plugged it back in and I had spark again. So I knew it wasnt that. I checked the timing and sure enough, it was off....again. So after repositioning the timing it fired up and now it purrs like a kitten. So for Bored400, dont be scared. Just make sure you triple check everything and take your time. This was not my first engine rebuild, but it was my first pull-rebuild-put back in and make run though. But I did figure everything out thanks to NAXJA and a mechanic father. Thanks for the help guys.
 
That plug could be to anything. Perhaps to a temp sensor for an overhead console. All of the XJ's used the same wiring harness, regardless of what options were installed.

I guess it was easier to make one harness than many, and made it easier for the mechanics to upgrade the Jeep with features later on.
 
My friend has a stroker that we rebuilt and it has the same symtoms that yours did... So can you explain how you fixed the timing? Pictures would help also. If it is easier you can email me a [email protected]

Thanks
Kevin
 
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